No 21 year old (adult) mother will have to give up their baby for the sole reason that they got pregnant by a 16/17 year old. Is someone threatening this? Do they desire and intend to raise the child together? These are the more important questions going forward because these people will forever be the child's biological parents.
Attorney Colson got it right in that no one would force the 21 yo to give up the child on the face of the information provided.
However, of note is the possibility of charges being sought against the 21 yo for having had sex with an individual who was below the age of majority. If this matter gets to the authorities, the 21 yo may face criminal charges including risk of injury, sexual assault and the like. If those charges are pursued, that could result in DCF intervention, which could result in the child being taken away from her, and placed with someone else (if someone volunteers from his side, the child would likely be placed with them). More information is needed to properly assess that side of the question.